What The Heck Is Racemic Epinephrine?

What The Heck Is Racemic Epinephrine?

So there are a few common points of confusion that I have noticed when it comes to epinephrine. One of them is in regard to the dilution of epinephrine, and the other deals with racemic epinephrine. First, I will attempt to explain what the different dilutions of epinephrine actually mean.

What does Epi 1:1000 mean?

Most of us are intimately familiar with the 1:1000 concentration of epinephrine, which is an emergency medicine staple. We know that there is 1 mg in each mL, but where does the 1000 come into play? The answer is fairly simple, but requires an explanation of a few basic assumptions about water first.

In order to better explain these assumptions, I decided to draw it out on my whiteboard. The drawing below shows that one cubic centimeter (1 cc) of water (H2O) (which is equivlent to 1 mL) weighs 1 gram under ideal conditions. Therefore, one gram of substance per mL of solution is equal to a 100% concentration of that substance, which, in this case, is water.

Now onto epinephrine. In the 1:1000 concentration, we are presented with a ratio that tells us that there is 1 g of epinephrine for every 1,000 mL. Another way we could say this is that there is one thousandth of a gram in every mL. What is one thousandth of a gram? Right! A MILLIGRAM! If you wanted to name the percentage of the concentration, you can simply move the decimal place of the total mass of epinephrine in one mL to the right twice (multiplying by 100). In this case, we have a 0.1% epinephrine solution.

What does epinephrine 1:10,000 mean?

Now that we understand what the ratio indicates, we can easily determine what epi 1:10,000 actually contains. Try it yourself, and then have a look at my whiteboard drawing below.

Hopefully I did not over-complicate this, conversions can be challenging, and make room for errors. For this reason it is always good to leave your ego at home, and have someone check your math, particularly when administering a powerful medication such as epinephrine. Now, lets talk about racemic epinephrine.

What the heck is racemic epinephrine?

I am going to stay out of the weeds on this one, and just put this as simply as possible. The shape of a particular drug molecule largely determines its effect on the sites, cells, or tissue it affects. “Regular” epinephrine, the type we are most familiar with, may be called L-Epinephrine because it is the levorotary version of epinephrine. We can just think of this as “left-handed epi”. Racemic epinephrine, on the other hand (no pun intended) contains both L-Epinephrine, AND D-Epinephrine. The “D” stands for dextrorotary, which we can think of as “right-handed Epi”. The D-Epinephrine is simply a mirror image of the L-epinephrine.

How do you make racemic epinephrine in the field?

I have heard ruminations that it is possible to “make” racemic epinephrine in the field. This is just not realistic. I have been told that, in order to make racemic epinephrine, dilute 1 mL of 1:1000 epinephrine in 3 mL of normal saline. This, I believe, is where the confusion is. Take a look at the package of racemic epinephrine in the image below.

Do you notice anything greatly different from “regular” epi? That’s right! The concentration! Racemic epinephrine is typically dispensed in a 2.25% concentration – that’s 22.5 mg/mL!!! The package instructions usually state that the medication should be diluted in, you guessed it, 3 mL of normal saline prior to administration via nebulizer.

So that is where I believe the myth of “making racemic epi” in the field came from. Current research tells us that administering 1:1000 epinephrine can be done safely without dilution via small volume nebulizer. Additionally, it appears to be just as, and possibly more effective than, racemic epinephrine for the treatment of croup. (It is now known that the R-Isomer of epinephrine is not actually active, meaning racemic epi is only more potent due to it’s concentration) Check out my article on Field Diagnosis and Treatment of Croup for more on this topic.

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